Present day radars use physically separate microwave devices to perform the receiver protecting function, the automatic gain function, and the sensitivity time control function. Receiver protecting is commonly accomplished by a device which functions as a high power limiter during the time when the radar is transmitting high power bursts. It prevents the power reflected toward the receiver from the radar antenna from burning out the receiver. When the transmitter burst ceases, the radar waits for the weak return echo from the target. This weak echo is received by the antenna and passes thru the TRLL (transmit-receive-tube-limiter-limiter function). The TRLL may be alternately thought of as an RP (receiver protector) which is newer and more descriptive terminology. Structurally it usually includes a plasma high power stage and a diode low power stage. The weak microwave echo may be acted upon by various system functions such as STC (sensitivity time control) or AGC (automatic gain control).
As aforementioned, receiver protector (RP), automatic gain control (AGC) and sensitivity time control (STC) functions have always been performed by separate physical components. It is the purpose of this invention to uniquely combine their functions into one physical component in such a manner as to significantly reduce the RF insertion loss. This loss directly contributes to receiver degradation, and its minimization is critical to overall system noise figure since it is located before the radar mixer and/or LNA (low noise microwave amplifier). The TRL (transmit receive limiter) is used as the receiver protector and the STC is used to program receiver gain so that it is low for targets at close range and high for targets at long range. The AGC is required to provide constant gain independent of received signal strength.